Process for forming deposited film by use of alkyl aluminum hydride

ABSTRACT

A process and apparatus for forming an Al film of good quality according to the CVD method utilizing the reaction between alkyl aluminum hydride and hydrogen, which is an excellent deposited film formation process also capable of selective deposition of Al. Pressure in a deposition chamber is maintained from 10 -3  to 760 Torr. Alkyl aluminum hydride and hydrogen gas are introduced at a partial pressure from 1.5×10 -5  to 1.3×10 -3  of the pressure in the chamber. Aluminum is deposited on a substrate in the chamber by heating the substrate sufficiently to decompose the alkyl aluminum hydride.

This application is a continuation of application Ser. No. 08/580,486filed Dec. 29, 1995, now abandoned, which is a divisional of Ser. No.08/264,498 filed Jun. 23, 1994, abandoned, which is a divisional of Ser.No. 07/902,829 filed Jun. 23, 1992, now U.S. Pat. No. 5,328,873, whichis a division of application Ser. No. 07/578,672 filed Sep. 7, 1990, nowU.S. Pat. No. 5,179,042.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for forming a deposited film,particularly a process for forming an Al deposited film which can bepreferably applied to electrodes or wiring of a semiconductor integratedcircuit device, etc.

2. Related Background Art

In the prior art, in electronic devices or integrated circuits usingsemiconductors, aluminum (Al) has been primarily used for electrodes andwiring. Al has many advantages. It is inexpensive and high inelectroconductivity, it can also be internally chemically protectedbecause a dense oxidized film can be formed on the surface, and it hasgood adhesion to Si, etc.

To form Al film for electrodes and wiring of Al or alloy as mentionedabove, has used the prior art the sputtering method such as magnetronsputtering, etc. However, since sputtering is generally a physicaldeposition method based on flying sputtered particles in a vacuum, thefilm thickness at the stepped portion or the insulating film side wallbecomes extremely thin, which can lead to a wire breaking in an extremecase. Nonuniformity of film thickness or wire breakage has the drawbackthat the reliability of Large Scale Integration LSI is markedlydecreased.

On the other hand, as the degree of integration of the integratedcircuits such as LSI, etc. increases, and miniaturization of wiring ormulti-layer wiring has been required in recent years, there areincreased demands which are not met by the Al wiring of the prior art.With greater miniaturization are increased degree of integration thesurface of LSI, etc. is subject to excessive unevenness due tooxidation, diffusion, thin film deposition, and etching, etc. Forexample, electrodes or wiring metal must be deposited on the surfacewith a stepped difference, or deposited in a through-hole which is verysmall in diameter and deep. In 4 Mbit or 16 Mbit DRAM (dynamic RAM),etc., the aspect ratio (through-hole depth/through-hole diameter) ofthrough-hole in which a metal composed mainly of Al such as Al, Al-Si,etc. is to be deposited is 1.0 or more, and the through-hole diameteritself becomes 1 μm or less. Therefore, even for a through-hole with alarge aspect ratio, a technique which can deposit a metal is required.

In particularly, to ensure an electrical connection to the device undera insulating film such as SiO₂, etc., rather than film formation, Almust be deposited to embed only the through-hole of the device. In sucha case, a method of depositing Al only on Si or metal surface, and notdepositing it on an insulating film such as SiO₂, etc. is required.

Such selective deposition or selective growth cannot be realized by thesputtering method which has been used in the prior art.

The bias sputtering method in which a bias is applied on a substrate anddeposition is performed to embed Al or an Al alloy only in thethrough-hole by utilizing the sputter-etching action and the depositionaction on the substrate surface has been developed. However, since abias voltage of some 100 V or higher is applied on the substrate, thedevice is adversely affected because of charged particle damage such asa change in the threshold of MOSFET, etc. Also, because both etching anddeposition action are present, there is the problem that the depositionspeed cannot be improved.

In order to solve the problems described above, various types of CVD(Chemical Vapor Deposition) methods have been proposed. In thesemethods, chemical reaction of the starting gas in some form is utilized.In plasma CVD or optical CVD, decomposition of the starting gas occursin the gas phase, and the active species formed there further reacts onthe substrate to form a film. In these CVD methods, due to the reactionin the gas phase, surface coverage on unevenness on the substratesurface is good. However, carbon atoms contained in the starting gasmolecules are incorporated into the film. Also, particularly in plasmaCVD, there was also damage by charged particles (so called plasmadamage) as in the case of the sputtering method.

The thermal CVD method, in which the film grows through the surfacereaction primarily on the substrate surface, provides good surfacecoverage on unevenness such as the stepped portion of the surface, etc.Also, it can be expected that deposition within the through-hole willreadily occur. Further, wire breakage at the stepped portion can beavoided.

For such reasons, as the formation method of the thermal CVD method hasbeen studied as the formation method for Al film. To form Al film usinggeneral thermal CVD, a method of transporting an organic aluminumdispersed in carrier gas to a heated substrate and pyrolyzing the gasmolecules on the substrate to form a film is known. For example, inJournal of Electrochemical Society, Vol. 131, p. 2175 (1984), by use oftriisobutyl aluminum (i-C₄ H₉)₃ Al (TIBA) as the organic aluminum gas,film formation is effected at a film formation temperature of 260° C.and a reaction tube pressure of 0.5 torr to form a film of 3.4 μohm.cm.

Japanese Laid-open Patent Application No. 63-33569 describes a method offorming a film by using no TiCl₄, but using in place thereof organicaluminum such as TIBA and heating it in the vicinity of the substrate.According to this method, Al can be deposited selectively only on themetal or semiconductor surface from which the naturally oxidized filmhas been removed.

In this case, it is clearly stated that the step of removing thenaturally oxidized film on the substrate surface is necessary beforeintroduction of TIBA. Also, since TIBA can be used alone, no carrier gasis required, but Ar gas may be used as the carrier gas. However, thereaction of TIBA with another gas (e.g. H₂) is not contemplated, andthere is no description of use of H₂ as the carrier gas. Also, inaddition to TIBA, trimethyl aluminum (TMA) and triethyl aluminum (TEA)are mentioned, but there is no specific description of other organicmetals. This is because, since the chemical properties of organic metalsgenerally vary greatly if the organic substituent attached to the metalelement varies, it is necessary to conduct detailed experimentation todetermine what organic metal should be used.

In the CVD method as described above, not only is there an inconveniencethat the naturally oxidized film must be removed, but also there is thedrawback that surface smoothness can not be obtained. Also, there is therestriction that heating the gas is necessary, and heating must be donein the vicinity of the substrate. It must also be experimentallydetermined at what proximity to the substrate the heating must be done.Therefore there is also the problem that placement for the heater cannotbe freely chosen.

In the pre-text of the 2nd Symposium of Electrochemical Society, Branchof Japan (Jul. 7, 1989), on page 75, film formation of Al according tothe double wall CVD method. In this method is described, TIBA is usedand the device is designed so that the gas temperature of TIBA can bemade higher than the substrate temperature. This method may be alsoregarded as a modification of the above-mentioned Japanese Laid-openPatent Application No. 63-33569. Al can be selectively grown only on ametal or semiconductor in this method, but the difference between thegas temperature and the substrate surface temperature is controlled withdifficulty, and there is the drawback that the bomb and the pipelinealso be heated. Moreover, according to this method, no uniformcontinuous film can be formed, smoothness of the film is poor, Alselective growth cannot be maintained for a long time, etc., unless thefilm is made thick.

As described above, prior art methods cannot readily provide selectivegrowth of Al, and even if possible, there is a problem with respect tosmoothness, resistance, purity, etc. of the Al film formed. Also, thereis the problem that the film formation method is complicated anddifficult to control.

SUMMARY OF THE INVENTION

As described above, in the technical field of semiconductors wherehigher integration has been desired in recent years, to inexpensivelyprovide a semiconductor device which is more highly integrated and hasimproved performances, there remained much room for improvement.

The present invention has been accomplished in view of the technicaltasks described above, and an object of the present invention is toprovide a process for forming a deposited film which can form an Al film(hereinafter referring comprehensively to pure Al and a metal composedmainly of Al) of good quality as the electroconductive material at adesired position with good controllability.

Another object of the present invention is to provide a process forforming a deposited film which can obtain an Al film which has extremelybroad general purpose utility and yet is of good quality, withoutrequiring a particularly complicated and expensive deposited filmforming device.

Still another object of the present invention is to provide a processfor forming a deposited film which can form an Al film with excellentsurface characteristics, electrical characteristics, purity, etc.according to the CVD method utilizing alkyl aluminum hydride andhydrogen.

Still another object of the present invention is to provide a processfor forming a deposited film of an Al film which has extremely broadgeneral purpose utility and excellent selectivity, without requiring aparticularly complicated and expensive deposited film forming device.

Still another object of the present invention is to provide a processfor forming a deposited film which can form an Al film under goodselectivity according to the CVD method utilizing alkyl aluminum hydrideand hydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view for illustration of a suitable deposited filmforming device in practicing the deposited film forming processaccording to the present invention.

FIG. 2 is a schematic view for illustration of another suitabledeposited film forming device in practicing the deposited film formingprocess according to the present invention.

FIGS. 3A-3E are schematic sectional views for illustration of thedeposited film forming process according to one embodiment of thepresent invention.

FIG. 4 is a chart showing the X-ray diffraction pattern of the Si (111)substrate having the Al film obtained according to the deposited filmforming process of the present invention.

FIGS. 5A and 5B are charts showing the X-ray diffraction pattern of theAl film on the Si (111) substrate obtained according to the depositedfilm forming process of the present invention.

FIG. 6 is a chart showing the X-ray diffraction pattern on the Si (100)substrate having the Al film obtained according to the deposited filmforming process of the present invention.

FIG. 7 is a schematic view for illustration of the scanning μ-RHEEDmethod.

FIG. 8 is a schematic view for illustration of the scanning μ-RHEEDmethod.

FIG. 9 is a chart showing another example of the X-ray diffractionpattern of the substrate having the Al film obtained according to theselective deposited film forming process of the present invention.

FIGS. 10A-10C are schematic views showing an example of the scanningsecondary electron image and the scanning μ-RHEED image of the substratehaving the Al film obtained according to the selective deposited filmforming process of the present invention.

FIG. 11 is a chart showing another example of the X-ray diffractionpattern of the substrate having the Al film obtained by the selectivedeposited film forming process of the present invention.

FIGS. 12A-12C are schematic views of another example of the scanningsecondary electron image and the scanning μ-RHEED image of the substratehaving the Al film obtained according to the selective deposited filmforming process of the present invention.

FIGS. 13A-13D are illustrations for explaining the mechanism of Aldeposition according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments according to the present invention are describedin detail below, but the present invention is not limited by theseembodiments, and it may have a constitution which accomplishes theobject of the present invention.

One preferred embodiment of the present invention is a process forforming a deposited film comprising the steps of:

(a) providing a substrate having an electron donative surface (A) in aspace for formation of the deposited film;

(b) introducing a gas of an alkyl aluminum hydride and hydrogen gas intothe space for formation of the deposited film; and

(c) maintaining the temperature of the electron donative surface (A)within the range of from the decomposition temperature of the alkylaluminum hydride to 450° C. to form an aluminum film on the electrondonative surface (A).

Further, another preferred embodiment of the present invention is aprocess for forming a deposited film comprising the steps of:

(a) providing a substrate having an electron donative surface (A) and anelectron non-donative surface (B) in a space for formation of thedeposited film;

(b) introducing a gas of an alkyl aluminum hydride and hydrogen gas intothe space for formation of the deposited film; and

(c) maintaining the temperature of the electron donative surface (A)within the range of from the decomposition temperature of the alkylaluminum hydride to 450° C. to form an aluminum film selectively on theelectron donative surface (A).

In the following, prior to detailed description, first, the process forforming a deposited film by use of an organic metal is outlined.

The decomposition reaction of an organic metal, and hence the thin filmdeposition reaction will vary greatly depending on the kind of the metalatom, the kind of the alkyl bonded to the metal atom, the means ofcausing the decomposition reaction to occur, the atmospheric gas, etc.

For example, in the case of M-R₃ (M: the group III metal, R: alkylgroup), trimethyl gallium: ##STR1## in thermal decomposition undergoesradical cleavage wherein Ga-CH₃ bond is cleaved, while triethyl gallium:##STR2## in thermal decomposition is decomposed through β-eliminationinto: ##STR3## and C₂ H₄. On the other hand, triethyl aluminum attachedwith the same ethyl group: ##STR4## in thermal decomposition undergoesradical decomposition in which Al-C₂ H₅ is cleaved. However,tri-iso-butyl aluminum having iC₄ H₉ bonded therein: ##STR5## is subjectto β-elimination.

Trimethyl aluminum (TMA) comprising CH₃ groups and Al has a dimerstructure at room temperature: ##STR6## and thermal decomposition isradical decomposition in which Al-CH₃ group is cleaved, and at atemperature of 150° C. or lower, it reacts with atmospheric H₂ to formCH₄, and forms finally Al.

However, at a high temperature of 300° C. or higher, even if H₂ may bepresent in the atmosphere the, CH₃ group will withdraw H from the TMAmolecule, until finally an Al-C compound is formed.

Also, in the case of TMA, in light or a certain region controlled inelectric power in H₂ atmosphere high frequency (ca. 13.56 MHz) plasma,C₂ H₆ will be formed by the bridging CH₃ between two Al's.

In essence, since even an organic metal comprising a CH₃ group which isthe simplest alkyl group on, C₂ H₅ group or iC₄ H₉ group and Al or Gahas a reaction mode depending on the kind of the alkyl group, the kindof the metal atom, the excitation decomposition means. For deposition ofa metal atom from an organic metal on a desired substrate, thedecomposition reaction must be strictly controlled. For example, when Alis to be deposited from triisobutyl aluminum: ##STR7## in the lowpressure CVD method comprising mainly thermal reaction, unevenness of μmorder is formed on the surface, whereby the surface morphology isinferior. Also, hillock generation by heat treatment, Si surfaceroughening through Si diffusion at the interface between Al and Sioccur, and also migration resistance is inferior, whereby it isdifficult to use this method for an ultra-LSI process.

For this reason, a method for controlling precisely both the gastemperature and the substrate temperature has been attempted. However,the device is complicated, and the method is of the sheet treatment typein which deposition can be effected only on one wafer by one depositionprocess. Besides, since the deposition speed is 500 Å/min. at thehighest, the throughput necessary for bulk production cannot berealized.

Similarly, when TMA is employed, Al deposition has been attempted by useof plasma or light, the device becomes complicated due to use of plasmaor light. Due to the sheet type device, there remains room forimprovement of throughput.

Dimethyl aluminum hydride (DMAH) as the alkyl aluminum hydride to beutilized in the present invention is a substance known as an alkylmetal, but what Al thin film would be deposited depends on the reactionmode, unless a deposited film is formed under all conditions. Forexample, in an example of depositing Al by optical CVD from DMAH, thesurface morphology is inferior, and the resistivity value was greaterthan the bulk value (2.7 μohm.cm) as several μohm to 10 μohm.cm, thusbeing inferior in film quality.

Now, referring to the drawings, preferred embodiments of the presentinvention are described in more detail.

In the present invention, to selectively deposit an Al film of goodquality as the electroconductive deposition film on a substrate, the CVDmethod is used.

More specifically, by use of dimethyl aluminum hydride (DMAH): ##STR8##as the alkyl aluminum hydride which is an organic metal or monomethylaluminum hydride (MMAH₂): ##STR9## as the alkyl aluminum hydride as thestarting gas containing at least one atom which becomes the constituentof the deposited film, and H₂ as the reaction gas, an Al film is formedby gas phase growth with a gas mixture of these on a substrate.

As the substrate in the present invention, a material having an electrondonative surface may be employed.

The electron donative material is described in detail below.

The electron donative material refers to one having existing or freeelectrons intentionally formed in the substrate, for example, a materialhaving a surface on which the chemical reaction is promoted throughgive-and-take of electrons with the starting gas molecules attached onthe substrate surface. For example, generally metals and semiconductorscorrespond to such a material. Those having a very thin oxidized film onthe metal or semiconductor surface are also included. With such a thinfilm, the chemical reaction can occur between the substrate and theattached starting molecules.

Specifically, there may be included semiconductors such asmonocrystalline silicon, polycrystalline silicon, amorphous silicon,etc., binary system or ternary system or quaternary system III-Vcompound semiconductors comprising combinations of Ga, In, Al as thegroup III element and P, As, N as the group V element, or II-IV compoundsemiconducters, or metals themselves such as tungsten, molybdenum,tantalum, aluminum, titanium, copper, etc., or silicides of the abovemetals such as tungsten silicide, molybdenum silicide, tantalumsilicide, aluminum silicide, titanium silicide, etc. Further metalscontaining either one of the constituent of the above metals such asaluminum silicon, aluminum titanium, aluminum copper, aluminum tantalum,aluminum silicon copper, aluminum silicon titanium, aluminum palladium,titanium nitride, may be used etc.

On the substrate with such a constitution, Al is deposited only throughsimple thermal reaction in the reaction system of the starting gas andH₂. For example, the thermal reaction in the reaction system betweenDMAH and H₂ may be basically considered as follows: ##STR10## DMAHassumes a dimer structure at room temperature. Also, with MMAH₂, a highquality Al film could be formed by thermal reaction as shown below inthe Examples.

Since MMAH₂ has low vapor pressure 0.01 to 0.1 Torr at room temperature,it is difficult to transport a large amount of the starting material andthe upper limit value of the deposition speed is several hundred Å/min.in the present embodiment. Preferably, it is most desirable to use DMAHwhich has a vapor pressure of 1 Torr at room temperature.

In another embodiment of the present invention, the CVD method is usedfor selective deposition of a good Al film as the electroconductivedeposition film on the substrate.

More specifically, as described above, by use of dimethyl aluminumhydride (DMAH) or monomethyl aluminum hydride (MMAH₂) and H₂ as thereaction gas, an Al film is selectively formed on the substrate by gasphase growth with a gas mixture of these.

The substrate applicable in the present invention has a first substratesurface material for formation of the surface on which Al is deposited,and a second substrate surface material on which no Al is deposited.And, as the first substrate surface material, a material having theelectron donative surface is used.

The material for forming the surface on which Al is not depositedselectively, namely the material for forming the electron non-donativesurface, conventional insulating materials, oxidized silicon formed bythermal oxidation, CVD, etc., glass or oxidized film such as BSG, PSG,BPSG, etc., thermally nitrided film, silicon nitrided film by plasmaCVD, low pressure CVD, ECR-CVD method, etc. may be used.

FIG. 1 is a schematic view showing a preferable deposition film formingdevice for applying the present invention.

Here, 1 is a substrate for forming an Al film. The substrate 1 ismounted on a substrate holder 3 provided within the reaction tube 2 forforming a space to form a deposited film which is substantially closed.As the material constituting the reaction tube 2, quartz is preferable,but it may be also made of a metal. In this case, it is preferable tocool the reaction tube. The substrate holder 3 is made of a metal, andis provided with a heater 4 so that the substrate can be heated. Thesubstrate temperature can be controlled by controlling the heatgeneration temperature of the heater 4.

The feeding system of gases is described below.

5 is a gas mixer, in which the starting gas and the reaction gas aremixed. The mixture is fed into the reaction tube 2. 6 is a starting gasgasifier provided for gasification of an organic metal as the startinggas.

The organic metal to be used in the present invention is liquid at roomtemperature, and is formed into saturated vapor by passing a carrier gasthrough the liquid of the organic metal within the gasifier 6, which isin turn introduced into the mixer 5.

The evacuation is constituted as described below.

7 is a gate valve, which is opened when performing evacuation of a largevolume such as during evacuation of the reaction tube 2 before formationof the deposited film. 8 is a slow leak valve, which is used whenperforming evacuation of a small volume such as in controlling thepressure internally of the reaction tube 2 during formation of thedeposited film. 9 is an evacuation unit, which is a pump for evacuationsuch as a turbo molecular pump, etc.

The conveying system of the substrate 1 is described below.

10 is a substrate conveying chamber which can house the substrate beforeand after formation of the deposited film, which is evacuated by openingthe valve 11. 12 is an evacuation unit for evacuating the conveyingchamber, which is a pump for evacuation such as a turbo molecular pump,etc.

The valve 13 is opened only when the substrate 1 is transferred betweenthe reaction chamber and the conveying space.

As shown in FIG. 1, in the starting gas gasifier 6 which is the chamberfor forming the starting gas, the liquid DMAH maintained at roomtemperature is bubbled with H₂ or Ar (or other inert gas) as the carriergas to form gaseous DMAH, which is transported to the mixer 5. The H₂gas as the reaction gas is transported through another route into themixer 5. The gas flow rates are controlled so that the respectivepartial pressures may become desired values.

In forming a film by this device, the starting gas may be MMAH₂, butDMAH with a vapor pressure enough to become 1 Torr at room temperatureis the most preferred. Also, DMAH and MMAH₂ may be used in a mixture.

The deposited film formed at a substrate temperature of 160° C. to 450°C. by use of such starting gas and reaction gas, with a thickness of forexample 400 Å, has a resistivity at room temperature of 2.7-3.0 μohm.cmwhich is substantially equal to Al bulk resistivity, and is a continuousand flat film. At this time, the pressure during film formation can bechosen within the range from 10⁻³ Torr to 760 Torr. Also, even when thefilm thickness may be 1 μm, its resistivity is ca. 2.7-3.0 μohm.cm, anda sufficiently dense film can be formed also with a relatively thickerfilm. Also, the reflectance in the visible light wavelength region isapproximately 80%, whereby a thin film with excellent surface flatnesscan be deposited.

The substrate temperature is desirably the decomposition temperature ofthe starting gas containing Al or higher, and 450° C. or lower asdescribed above, but specifically the substrate temperature of 200° to450° C. is more desirable, when deposition is carried out under thesecondition, by making the DMAH partial pressure 10⁻⁴ to 10⁻³ Torr, thedeposition speed becomes as great as 100 Å/min. to 800 Å/min., wherebysufficiently great deposition speed corresponds to the cost as the Aldeposition technique for ultra-LSI can be obtained.

A more preferable substrate temperature condition is 270° C. to 350° C.,and the Al film deposited under these condition is also stronglyorientatable and, even when subjected to the heat treatment at 450° C.for 1 hour, the Al film on the Si monocrystalline or Si polycrystallinesubstrate becomes a good Al film without generation of hillock, on spikeas seen in the film forming method of the prior art. Also, such an Alfilm has excellent electro-migration resistance.

In the device shown in FIG. 1, Al can be deposited on only one sheet ofsubstrate in deposition for one time. Although a deposition speed of ca.800 Å/min. can be obtained, it is still insufficient to performdeposition of a large number of sheets within a short time.

As the improved deposition film forming device, there is a low pressureCVD device which can deposit Al by simultaneous mounting a large numberof wafer sheets. Since the Al film formation according to the presentembodiment utilizes the surface reaction on the electron donativesubstrate surface, in the hot wall type low pressure CVD method whereinonly the substrate is heated, Al can be deposited on the substrate byuse of DMAH and H₂.

The reaction tube pressure may be 0.05 to 760 Torr, desirably 0.1 to 0.8Torr, the substrate temperature 160° C. to 450° C., desirably 200° C. to400° C., the DMAH partial pressure 1×10⁻⁵ -fold to 1.3×10⁻³ -fold of thepressure in the reaction tube, and under such conditions, Al can be welldeposited on the electron donative substrate.

FIG. 2 is a schematic illustration showing a deposited film formingdevice which is applicable to the present invention.

57 is a substrate for forming the Al film. 50 is an outside reactiontube made of quartz for forming a film formation space substantiallyclosed to the surroundings, 51 is an innerside reaction tube made ofquartz located for separating the flow of gas within the outsidereaction tube 50, 54 is a flange made of a metal for opening and closingthe opening of the outside reaction tube 50, and the substrate 57 islocated within the substrate holding member 56 provided within theinnerside reaction tube 51. The substrate holding member 56 should bepreferably made of quartz.

Also, in the present device, the substrate temperature can be controlledby the heater portion 59. The pressure internally of the reaction tube50 is constituted so as to be controllable by the evacuation systemconnected through the gas evacuation outlet 53.

The gas feeding system is constituted to have a first gas system, asecond gas system and a mixer (none are shown) similarly as the deviceshown by the symbols 5 and 6 in FIG. 1, and the starting gas and thereaction gas are introduced into the reaction tube 50 through thestarting gas inlet 52. These gases react on the surface of the substrate57 during passage within the innerside reaction tube 51 as shown by thearrowhead 58 in FIG. 2 to deposit Al on the substrate surface. After thereaction the gases pass through the gap formed between the innersidereaction tube 51 and the outside reaction tube 50, and are evacuatedthrough the gas evacuation outlet 53.

In taking the substrate out and in, the flange 54 made of a metal ispermitted to fall by an elevator (not shown) together with the substrateholding member 56 and the substrate 57 to be moved to a predeterminedposition where the substrate is mounted and detached.

By forming a deposited film under the conditions as described above, Alfilms of good quality can be formed in all the wafers within the device.

As described above, the film obtained according to the Al film formationprocess of the present invention is dense, with little content ofimpurity such as carbon, etc. and resistivity similar to bulk,resistivity and also has high surface smoothness, and therefore theremarkable effects described below can be obtained.

(1) Reduction of hillock

Hillock is occurrence of concavities on the Al surface due to partialmigration of Al when inner stress during film formation is released inthe heat treatment step. Also, similar phenomenon occurs by localmigration by current passage. The Al film formed by the presentinvention has little inner stress and is in the monocrystal line stateor close to that. For this reason, in the heat treatment at 450° C. forone hour, as contrasted to formation of 10⁴ -10⁶ /cm² of hillocks in theAl film of the prior art, the hillock number could be greatly improvedas 0 to 10/cm². Thus, due to substantial absence of Al surfaceconcavity, the resist film thickness and the interlayer insulating filmcan be made thin to be advantageous for making it finer and more flat.

(2) Improvement of electro-migration resistance

Electro-migration is the phenomenon that the wiring atoms move bypassage of a current of high density. By this phenomenon, voids aregenerated and grow along the grain boundary, whereby as accompanied by areduction of the cross-sectional area, the wiring is subject to thermaldecomposition.

Migration resistance is generally evaluated the average wiring life.

The wiring formed by the sputtering method or the CVD method of theprior art has an average wiring life of 1×10² to 10³ hours (in the caseof wiring with a cross-sectional area of 1 μm²) under the currentpassage test conditions of 250° C., 1×10⁶ A/cm². In contrast, the Alfilm obtained by the Al film formation method based on the presentinvention can obtain an average wiring life of 10³ to 10⁴ hours with awire having a cross-sectional area of 1 μm².

Hence, according to the present invention, for example, when the wiringwidth is 0.8 μm, a wiring layer thickness of 0.3 μm can withstandpractical application. That is, since the wiring layer can be madethinner, any unevenness on the semiconductor surface after arranging ofthe wiring can be suppressed to a minimum, and also ordinary current canbe passed with high reliability. This is possible by a very simpleprocess.

(3) Improvement of surface smoothness (improvement of wiring patterningcharacteristic)

In the prior art, roughness of the surface of a metal thin film causeddifficulties in aligning the mask and the substrate in the patterningstep and in the etching step.

That is, there was unevenness extending to several μm on the surface ofAl film according to the prior art method, whereby the surfacemorphology was poor, and therefore had the following disadvantages:

1) Alignment signals cause diffused reflection to occur at the surface,whereby noise level becomes higher and inherent alignment signals cannotbe discriminated.

2) To cover large surface unevenness, the resist film thickness must belarge, which is opposite to fine formation.

3) If the surface morphology is poor, halation due to the resistinternal reflection will occur locally, whereby resist remaining occurs.

4) If the surface morphology is poor, the side wall becomes notched inthe wiring etching step according to its unevenness.

According to the present invention, the surface morphology of Al film ismarkedly improved to prevent all the drawbacks described above.

(4) Improvement of resistance in contact hole and through hole and ofcontact resistance

In the prior art method, if the size of the contact hole becomes finerthan 1 μm×1 μm or less, Si in the wiring is precipitated on thesubstrate of the contact hole during heat treatment in the wiring stepto cover thereover, whereby resistance between the wiring and theelement becomes markedly larger.

According to the embodiment of the present invention, since a dense filmis formed according to the surface reaction, Al has been confirmed tohave a resistivity of 2.7-3.3 μohm cm. Also, the contact resistivity canattain 1×10⁻⁶ ohm.cm² at an area of 0.6 μm×0.6 μm when the Si portionhas an impurity of 10²⁰ cm⁻³.

That is, according to the present invention, a good contact with thesubstrate can be obtained.

In other words, in the patterning step, at the line width of theresolving power limit of the exposure machine, the alignment precision3σ=0.15 μm can be accomplished, whereby wiring having a smooth sideplane is rendered possible without causing halation to occur.

(5) It becomes possible to reduce the heat treatment during the wiringstep or to abolish the heat treatment step.

As described in detail above, by applying the present invention to thewiring formation method of a semiconductor integrated circuit, the yieldcan be improved, and cost can be reduced to a great extent as comparedwith Al wiring of the prior art.

FIGS. 3A-3E show how the Al film according to the present invention isselectively grown.

FIG. 3A is an illustration showing schematically the cross-section ofthe substrate before forming the Al deposited film according to thepresent invention. 90 is the substrate comprising an electron donativematerial, and 91 a thin film comprising an electron non-donativematerial.

In the case of using DMAH as the starting gas, when a gas mixturecontaining H₂ as the reaction gas is fed onto the substrate 90 heatedwithin a temperature range from the decomposition temperature of DMAH to450° C., Al is precipitated on the substrate 90, whereby a continuousfilm of Al is formed as shown in FIG. 3B. Here, the pressure within thereaction tube 2 should be desirably 10⁻³ to 760 Torr, and the DMAHpartial pressure preferably 1.5×10⁻⁵ to 1.3×10⁻³ -fold of the pressurewithin the above reaction tube.

When deposit ion of Al i s continued under the above conditions, via thestate of FIG. 3C, the Al film grows to the level of the uppermostportion of the thin film 91 as shown in FIG. 3D. Further, when grownunder the same conditions, as shown in FIG. 3E, the Al film can grow to5000 Å substantially without growth in the lateral direction. This isthe most characteristic point of the deposited film obtained by thepresent invention, and it will be understood how a film of good qualitycan be formed under good selectivity.

As the result of analysis according to Auger's electron spectroscopy orphotoelectric spectroscopy, no entrainment of an impurity such as carbonor oxygen is recognized in this film.

The deposited film thus formed has a resistivity of, for example, with afilm thickness of 400 Å, 2.7-3.0 μohm.cm at room temperature which issubstantially equal to the bulk resistivity of Al, and becomescontinuous and flat film. Also, even with a film thickness of 1 μm, itsresistance at room temperature is approximately 2.7-3.0 μohm.cm and asufficiently dense film is formed with a relatively thicker film. Thereflectance in the visible wavelength region is approximately 80%, and athin film with excellent surface flatness can be deposited.

The substrate temperature in performing such selective deposition shouldbe the decomposition temperature of the starting gas containing Al orhigher and 450° C. or lower as mentioned above, but specifically asubstrate temperature of 200° to 450° C. is desirable. When depositionis performed under such condition, the deposition speed is as great as100 Å/min. to 800 Å/min. when DMAH partial pressure is 10⁻⁴ to 10⁻³Torr. Thus a sufficiently great deposition speed can be obtained as theAl deposition technique for ultra-LSI.

A more preferable substrate temperature condition is 270° C. to 350° C.,and the Al film deposited under this condition is also stronglyorientatable and, even when subjected to the heat treatment at 450° C.for 1 hour, the Al film on the Si monocrystalline or Si polycrystallinesubstrate becomes a good Al film without generation of hillock on spike.Also, such Al film is excellent in electro-migration resistance.

Similarly in the case of selective deposition, in the device shown inFIG. 1, Al can be deposited on only one sheet of substrate at a time.Although a deposition speed of ca. 800 Å/min. can be obtained, it isstill insufficient for performing deposition of a large number of sheetswithin a short time.

A low pressure CVD device can deposit Al by simultaneous mounting of alarge number of sheets of wafer. Since the Al film formation accordingto the present embodiment utilizes the surface reaction of the electrondonative substrate surface, in the hot wall type low pressure CVD methodwherein only the substrate is heated, Al can be deposited on thesubstrate by use of DMAH and H₂.

The reaction tube pressure may be 0.05 to 760 Torr, desirably 0.1 to 0.8Torr, the substrate temperature 160° C. to 450° C., desirably 200° C. to400° C., the DMAH partial pressure 1×10⁻⁵ fold to 1.3×10⁻³ -fold of thepressure in the reaction tube, and under such conditions, Al can beselectively deposited on only the electron donative substrate.

The deposited film forming device to which such present invention isapplicable is the same as in FIG. 2 described above, and therefore itsdetailed description is omitted here.

By forming a deposited film under the conditions as described above byuse of such device, Al films of good quality can be formed selectivelyand simultaneously in all the wafers within the device.

As described above, the film obtained according to the Al film selectiveformation process based on the embodiment of the present invention isdense with very little content of impurity such as carbon, etc. andresistivity which is similar to bulk, and also has high surfacesmoothness, and therefore remarkable effects as described below can beobtained.

(1) Reduction of hillock

The Al film formed according to the present invention has littleinternal stress and is under the state of monocrystal or approximate tothat. For this reason, in the heat treatment at 450° C. for one hour, ascontrasted to formation of 10⁴ -10⁶ /cm² of hillocks in the Al film ofthe prior art, the hillock number could be greatly improved as 0 to10/cm².

(2) Improvement of electro-migration resistance

The wiring formed by the method of the prior art has obtained an averagewiring life of 1×10² to 10³ hours (in the case of a wiringcross-sectional area of 1 μm²) under the current passage test conditionsof 250° C., 1×10⁶ A/cm². In contrast, the Al film obtained by the Alfilm selective formation method based on the embodiment of the presentinvention can obtain an average wiring life of 10³ to 10⁴ hours with awiring having a cross-sectional area of 1 μm².

(3) Reduction of alloy pit in contact portion

The Al selectively formed according to the present invention cansuppress generation of alloy pit at the contact portion with thesubstrate crystal even by the heat treatment during wiring step, andalso a wiring with good contact characteristic can be obtained. That is,even when the junction is made shallow to the extent of 0.1 μm, thejunction will not be destroyed with only the Al material.

(4) Improvement of surface smoothness (patterning characteristicimprovement of wiring)

According to the present invention, the surface morphology of the Alfilm to be formed can be improved, whereby all of the problems of theprior art can be improved.

That is, in the patterning step, at the line width of the resolvingpower limit of the exposure machine, the alignment precision 3σ=0.15 μmcan be accomplished, whereby wiring having smooth side plane is renderedpossible without causing halation to occur.

(5) Improvement of resistance in contact hole and through hole andcontact resistance

According to the present invention, since a dense film is selectivelyformed by the surface reaction even when the opening may be 1 μm×1 μm orless, it has been confirmed that the Al completely filled within thecontact hole and through hole each has a resistivity of 2.7-3.3 μohm.cm.Also, the contact resistivity can attain 1×10⁻⁶ ohm.cm² in the casewhere the Si portion has an impurity of 10²⁰ cm⁻³ in a hole of 0.6μm×0.6 μm.

That is, according to the present invention, the wiring material can becompletely embedded only in the minute opening, and also good contactwith the substrate can be obtained. Therefore, the present invention cancontribute greatly to improvement of resistance within hole and contactresistance which have been the greatest problems in the fine process of1 μm or less.

(6) It is possible to make the heat treatment temperature during wiringstep lower or to omit the heat treatment step.

As described in detail above, by applying the present invention to thewiring formation method of a semiconductor integrated circuit,particularly embedding of contact hole or through hole, the yield can beimproved, and cost can be reduced to great extent as compared with Alwiring of the prior art.

EXAMPLE 1

First, the procedure for Al film formation is as follows. By use of thedevice shown in FIG. 1, the reaction tube 2 is internally evacuated toca. 1×10⁻⁸ Torr by the evacuation unit 9. However, Al film can also beformed if the vacuum degree within the reaction tube 2 is higher than1×10⁻⁸ Torr.

After washing the Si wafer, the conveying chamber 10 is released toatmospheric pressure and Si wafer is mounted in the conveying chamber.The conveying chamber is evacuated to ca. 1×10⁻⁶ Torr, and then the gatevalve 13 is opened and the wafer is mounted on the wafer holder 3.

After mounting of the wafer on the wafer holder 3, the gate valve 13 isclosed, and the reaction chamber 2 is evacuated to a vacuum degree ofca. 1×10⁻⁸ Torr.

In this Example, DMAH is fed through the first gas line. As the carriergas of DMAH line H₂ which is the same as the reaction gas is employed.The second gas line is used for H₂.

By passing H₂ through the second gas line, the pressure within thereaction tube 2 is made a predetermined value by controlling the openingof the slow leak valve 8. A typical pressure in this Example is madeapproximately 1.5 Torr. Then, the wafer is heated by current passagethrough the heater 4. After the wafer temperature has reached apredetermined temperature, DMAH is introduced into the reaction tubethrough the DMAH line. The whole pressure is ca. 1.5 Torr, and the DMAHpartial pressure is made ca. 1.5×10⁻⁴ Torr. When DMAH is introduced intothe reaction tube 2, Al is deposited. After a predetermined depositiontime has elapsed, feeding of DMAH is stopped. Next, heating of theheater 4 is stopped to cool the wafer. Feeding of H₂ gas is stopped, andafter evacuation internally of the reaction tube, the wafer istransferred to the conveying chamber, and only the conveying chamber ismade atmospheric pressure before taking out the wafer. The outline of Alfilm formation is as described above.

EXPERIMENTAL EXAMPLE 1

Next, preparation of samples according to Example 1 is described.

130 Sheets of samples of monocrystalline Si substrates (N type, 1-2ohm.cm) were prepared, the substrate temperatures were set at 13 levels,and Al films were deposited at the respective temperatures each for 10sheets according to the procedure as described above under the followingconditions:

whole pressure: 1.5 Torr

DMAH partial pressure: 1.5×10⁻⁴ Torr.

The Al films deposited by varying the substrate temperature at 13 levelswere evaluated by use of various evaluation methods. The results areshown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Evalu-                                                                        ation                                                                              Substrate temperature (°C.)                                       item 150                                                                              160                                                                              200                                                                              250                                                                              270                                                                              300                                                                              330                                                                              350                                                                              370                                                                              400                                                                              430                                                                              450                                                                              470                                  __________________________________________________________________________    Carbon                                                                             -- 0  0-*                                                                              0  0  0  0  0  0  0  0  0  1˜9                            content                                                                       (%)                                                                           Resistivity                                                                        -- 2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7 ˜                                                                      2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                           (μΩ · cm)                                                           3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                  Reflect-                                                                           -- 85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        70 60 60                                   ance (%)                                                                              95 95 95 95 95 95 95 95 95    or or                                                                         lower                                                                            lower                                Average                                                                            -- 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                     wiring  10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                             life (hour)                                                                   Deposition                                                                         -- 1˜                                                                         100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       1000                                 Speed   9  800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                     (Å/min)                                                                   Hillock                                                                            -- 0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                             density 10.sup.3                                                                         10.sup.3                                                                         10.sup.3                                                                         10 10 10 10 10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                             (cm.sup.-2)                                                                   Spike                                                                              -- 0˜                                                                         0˜                                                                         0  0  0  0  0  0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                             generation                                                                            10 10                30 30 30 30 30                                   ratio (%)                                                                     __________________________________________________________________________     Note: No deposition occurs at substrate temperature of 150° C.         Average wiring life is time to wire breaking when current is passed at a      current density of 1 × 10.sup.6 A/cm.sup.2 through a crosssectional     area of 1 μm.sup.2 at 250° C.                                       Spike generation ratio is destruction probability at the junction portion     of 0.15 μm depth.                                                     

Al films of very good quality were obtained at a temperature range of160° C. to 450° C., more preferably 200° C. to 400° C., optimally 270°C. to 350° C.

EXAMPLE 2

By the evacuation unit 9, the reaction tube 2 is evacuated internally toca. 1×10⁻⁸ Torr. Al film can be formed even if the vacuum degree in thereaction tube 2 may be higher than 1×10⁻⁸ Torr.

After washing of the Si wafer, the conveying chamber 10 is released toatmospheric pressure and the Si wafer is mounted in the conveyingchamber. The conveying chamber is evacuated to ca. 1×10⁻⁶ Torr, then thegate valve 13 is opened and the wafer is mounted on the wafer holder 3.

After mounting of the wafer holder 3, the gate valve 13 is closed, andthe reaction chamber 2 is evacuated to a vacuum degree of ca. 1×10⁻⁸Torr.

In this Example, the first gas line is used for DMAH. As the carrier gasfor the DMAH line, Ar is employed. The second gas line is used for H₂.

By passing H₂ through the second gas line, the pressure within thereaction tube 2 is made a predetermined value by controlling the openingof the slow leak valve 8. A typical pressure in this Example is madeapproximately 1.5 Torr. Then, the wafer is heated by current passagethrough the heater 4. After the wafer temperature has reached apredetermined temperature, DMAH is introduced into the reaction tubethrough the DMAH line. The whole pressure is ca. 1.5 Torr, and the DMAHpartial pressure is made ca. 1.5×10⁻⁴ Torr. When DMAH is introduced intothe reaction tube 2, Al is deposited. After a predetermined depositiontime has elapsed, feeding of DMAH is stopped. Next, heating of theheater 4 is stopped to cool the wafer. Feeding of H₂ gas is stopped, andafter evacuating the reaction tube, the wafer is transferred to theconveying chamber, and only the conveying chamber is made atmosphericpressure before taking out the wafer. The outline of Al film formationis as described above.

EXPERIMENTAL EXAMPLE 2

Al films were formed according to the method of Example 2. For the filmsobtained, the resistivity, carbon content, average wiring life,deposition speed, hillock density, generation of spike and reflectance,were the same in Example 1.

EXAMPLE 3

Example 3 performs deposition according to the same procedure by usingMMAH₂ as the starting gas by setting the conditions as follows:

whole pressure: 1.5 Torr

MMAH₂ partial pressure: 5×10⁻⁴ Torr.

EXPERIMENTAL EXAMPLE 3

According to the method of the above Example 3, films were formed byvarying the substrate temperature within a temperature range from 160°C. to 400° C. As the result, Al thin films excellent in flatness,denseness, and containing no carbon impurity were deposited similarly asin Experimental example 1.

EXAMPLE 4

This Example 4 is a film formation according to the low pressure CVDmethod.

EXPERIMENTAL EXAMPLE 4

A monocrystalline silicon substrate was placed in the low pressure CVDdevice shown in FIG. 2, and Al film was formed within the same badge.The film formation conditions were a reaction tube pressure of 0.3 Torr,a DMAH partial pressure of 3.0×10⁻⁵ Torr, a substrate temperature of300° C., and a film formation time of 10 minutes.

Conditions. An Al film of 7000 Å was deposited. The film quality wasvery good, exhibiting the same properties as one prepared at a substratetemperature of 300° C. shown in Experimental example 1.

EXPERIMENTAL EXAMPLE 5

Samples having Al films formed according to the same method as inExample 1 were prepared. When crystallinity of the Al film deposited onthe Si wafer of the respective samples, was examined by use of the X-raydiffraction method and the reflective electron beam diffraction method,it was found to be a monocrystalline Al.

First, the evaluation methods are described.

When the crystal direction of the Si substrate is (111) plane, fromX-ray diffraction, as shown in FIG. 4, only the diffraction peak showingAl (100) was observed. In reflective high speed electron beamdiffraction by use of an acceleration voltage of 80 kV or 100 kV, asshown in FIG. 5, a monocrystal spot showing Al (100) was observed. FIG.5A is a diffraction pattern when an electron beam is permitted to enterAl (100) in the 001! direction. FIG. 5B a diffraction pattern when anelectron beam is permitted to enter Al (100) in the direction of 011!.Thus, the Al film on the Si (111) substrate was found to be amonocrystal having a (100) plane. Within the substrate temperature rangein Table 1, particularly those deposited at a range from 250° C. to 330°C. were found to have Al films deposited which were stablymonocrystalline.

Also, the Al films deposited on the Si (111) substrate with thesubstrate surface having off-angles differing by 1°, 2°, 3°, 4°, 5° fromthe Si (111) plane were also found to have Al (100) monocrystalsdeposited stably, particularly under the temperature conditions of thesubstrate temperature ranging from 250° C. to 330° C., as in the casewhen deposited on the Si (111) substrate as described above.

When the crystal direction of the Si substrate is (100) plane, fromX-ray diffraction, as shown in FIG. 6, only the diffraction peak showingAl (111) was observed. In reflective high speed electron beamdiffraction, by use of an acceleration voltage of 80 kV or 100 kV, amonocrystal spot showing Al (111) was observed. Thus, the Al film on theSi (100) substrate was found to be a monocrystal having (111) plane.Within the substrate temperature range in Table 1, particularly thosedeposited at a range from 250° C. to 330° C., were found to have Alfilms deposited which were stably monocrystalline. Also, the Al filmsdeposited on the Si (100) substrate with the substrate surface havingoff-angles differing by 1°, 2°, 3°, 4°, 5° from the Si (100) plane werealso found to have Al (111) monocrystals deposited stably, particularlyunder the temperature conditions of the substrate temperature rangingfrom 250° C. to 330° C., as in the case when deposited on the Si (111)substrate as described above.

EXPERIMENTAL EXAMPLE 6

Crystallinities of the Al films formed according to the method ofExample 2 were evaluated. Similarly as in the case of Example 5,particularly within the range of the substrate temperature from 250° C.to 330° C., Al (100) monocrystals were formed on the Si (111) substrate,and Al (111) monocrystal on the Si (100) substrate.

EXPERIMENTAL EXAMPLE 7

Al films were formed on Si substrate according to the method of Example3. As the result of evaluation of crystallinities of the Al films by theX-ray diffraction method and the reflective high speed electron beamdiffraction method, the following results were obtained.

When the crystal direction of the Si substrate surface is (111) plane,from X-ray diffraction, as shown in FIG. 4, only the diffraction peakshowing Al (100) was observed. In reflective high speed electron beamdiffraction by use of an acceleration voltage of 80 kV or 100 kV, asshown in FIG. 5, a monocrystal spot showing Al (100) was observed. Thus,the Al film on the Si (111) substrate was found to be a monocrystalhaving (100) plane.

Also, the Al films deposited on the Si (111) substrate with thesubstrate surface having off-angles differing by 1°, 2°, 3°, 4°, 5° fromthe Si (111) plane were also found to have Al (100) monocrystalsdeposited, as in the case when deposited on the Si (111) substrate asdescribed above.

When the crystal direction of the Si substrate is (100) plane, fromX-ray diffraction, as shown in FIG. 6, only the diffraction peak showingAl (111) was observed. In reflective high speed electron beamdiffraction by use of an acceleration voltage of 80 kV or 100 kV, amonocrystal spot showing Al (111) was observed. Thus, the Al film on theSi (100) substrate was found to be a monocrystal having (111) plane.Also, the Al films deposited on the Si (100) substrate with thesubstrate surface having off-angles differing by 1°, 2°, 3°, 4°, 5° fromthe Si (100) plane were also found to have Al (111) monocrystalsdeposited, similarly as in the case when deposited on the Si (111)substrate as described above.

The Examples 6 to 8 and the Experimental examples 8 to 16 are exampleswhen forming Al films selectively.

EXAMPLE 5

First, the procedure or Al film formation according to this Example isas follows. By use of the device shown in FIG. 1, the reaction tube 2 isinternally evacuated to ca. 1×10⁻⁸ Torr by the evacuation unit 9.However, Al film can be also formed even if the vacuum degree within thereaction tube 2 may be higher than 1×10⁻⁸ Torr.

After washing of the Si wafer treated so as to effect selectivedeposition, the conveying chamber 10 is released to atmospheric pressureand the Si wafer is mounted in the conveying chamber. The conveyingchamber is evacuated to ca. 1×10⁻⁶ Torr, then the gate valve 13 isopened and the wafer is mounted on the wafer holder 3.

After mounting of the wafer on the wafer holder 3, the gate valve 13 isclosed, and the reaction chamber 2 is evacuated to 3 vacuum degree ofca. 1×10⁻⁸ Torr.

In this Example, DMAH is fed through the first gas line. As the carriergas of DMAH line, H₂ is employed. The second gas line is used for H₂. Bypassing H₂ through the second gas line, the pressure within the reactiontube 2 is made a predetermined value by controlling the opening of theslow leak valve 8. A typical pressure in this Example is approximately1.5 Torr. Then, the wafer is heated by current passage through theheater 4. After the wafer temperature has reached a predeterminedtemperature, DMAH is introduced into the reaction tube through the DMAHline. The whole pressure is ca. 1.5 Torr, and the DMAH partial pressureis made ca. 1.5×10⁻⁴ Torr. When DMAH is introduced into the reactiontube 2, Al is deposited. After a predetermined deposition time haselapsed, feeding of DMAH is stopped. Next, heating of the heater 4 isstopped to cool the wafer. Feeding of H₂ gas is stopped, and afterevacuation internally of the reaction tube, the wafer is transferred tothe conveying chamber, and only the conveying chamber is madeatmospheric pressure before taking out the wafer. The outline of Al filmformation is as described above.

EXPERIMENTAL EXAMPLE 8

Si substrates (N type, 1-2 ohm.cm) were subjected to thermal oxidationat a temperature of 1000° C. according to the hydrogen combustion system(H₂ : 4 liters/M, O₂ : 2 liters/M).

The film thickness was 7000 Å±500 Å, and the refractive index 1,46. Aphotoresist was coated on the whole Si substrate, and a desired patternwas baked by an exposure machine. The pattern was such that variousholes of 0.25 μm×0.25 μm-100 μm×100 μm were opened. After development ofthe photoresist, with the photoresist as the mask, the subbing SiO₂ wasetched by the reactive ion etching (RIE), etc. to have the substrate Sipartially exposed. Thus, 130 sheets of samples having various sizes ofSiO₂ holes of 0.25 μm×0.25 μm-100 μm×100 μm were prepared, the substratetemperature was set at 13 levels, and for the samples each of 10 sheetsat the respective temperatures, Al films were selectively depositedfollowing the procedure as described above under the followingconditions:

whole pressure: 1.5 Torr

DMAH partial pressure: 1.5×10⁻⁴ Torr.

The Al films deposited by varying the substrate temperature at 13 levelswere evaluated by use of various evaluation methods. The results areshown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Evalu-                                                                        ation                                                                              Substrate temperature (°C.)                                       item 150                                                                              160                                                                              200                                                                              250                                                                              270                                                                              300                                                                              330                                                                              350                                                                              370                                                                              400                                                                              430                                                                              450                                                                              470                                  __________________________________________________________________________    Carbon                                                                             -- 0  0  0  0  0  0  0  0  0  0  0  1˜                             content                                  9                                    (%)                                                                           Resistivity                                                                        -- 2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                                                                       2.7˜                           (μΩ · cm)                                                           3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                                                              3.3                                  Reflect-                                                                           -- 85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        85˜                                                                        70 60 60                                   ance (%)                                                                              95 95 95 95 95 95 95 95 95    or or                                                                         lower                                                                            lower                                Average                                                                            -- 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                                                                 10.sup.3 ˜                     wiring  10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                             life (hour)                                                                   Deposition                                                                         -- 1˜                                                                         100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       100˜                                                                       1000                                 Speed   9  800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                                                              800                                     (Å/min)                                                                   Hillock                                                                            -- 0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                             density 10.sup.3                                                                         10.sup.3                                                                         10.sup.3                                                                         10 10 10 10 10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                                                                         10.sup.4                             (cm.sup.-2)                                                                   Spike                                                                              -- 0˜                                                                         0˜                                                                         0  0  0  0  0  0˜                                                                         0˜                                                                         0˜                                                                         0˜                                                                         0˜                             generation                                                                            10 10                30 30 30 30 30                                   ratio (%)                                                                     __________________________________________________________________________     Note: No deposition occurs at substrate temperature of 150° C.         Average wiring life is time to wire breaking when current is passed at a      current density of 1 × 10.sup.6 A/cm.sup.2 through a crosssectional     area of 1 μm.sup.2 at 250° C.                                       Spike generation ratio is destruction probability at the junction portion     of 0.15 μm depth.                                                     

In the above samples, no Al was deposited on SiO₂ at a temperature rangefrom 160° C. to 450° C., and Al was deposited only on the portion withopening of SiO₂ to have Si exposed. Also, when deposition was carriedout in the above temperature range continuously for 2 hours, similarselective deposition was maintained.

EXAMPLE 6

By the evacuation unit 9, the reaction tube 2 is evacuated to ca. 1×10⁻⁸Torr. Al film can be formed even if the vacuum degree in the reactiontube 2 is higher than 1×10⁻⁸ Torr.

After washing the Si wafer, the conveying chamber 10 is released toatmospheric pressure and the Si wafer is mounted in the conveyingchamber. The conveying chamber is evacuated to ca. 1×10⁻⁶ Torr, then thegate valve 13 is opened and the wafer is mounted on the wafer holder 3.

After mounting of the wafer on the wafer holder 3, the gate valve 13 isclosed and the reaction chamber 2 is evacuated to a vacuum degree of ca.1×10⁻⁸ Torr.

In this Example, the first gas line is used for DMAH. As the carrier gasfor the DMAH line, Ar is employed. The second gas line is used for H₂.

By passing H₂ through the second gas line, the pressure within thereaction tube 2 is made a predetermined value by controlling the openingof the slow leak valve 8. A typical pressure in this Example isapproximately 1.5 Torr. Then, the wafer is heated by current passagethrough the heater 4. After the wafer temperature has reached apredetermined temperature, DMAH is introduced into the reaction tubethrough the DMAH line. The whole pressure is ca. 1.5 Torr, and the DMAHpartial pressure is made ca. 1.5×10⁻⁴ Torr. When DMAH is introduced intothe reaction tube 2, Al is deposited. After a predetermined depositiontime has elapsed, feeding of DMAH is stopped. Next, heating of theheater 4 is stopped to cool the wafer. Feeding of H₂ gas is stopped, andafter evacuation of the reaction tube, the wafer is transferred to theconveying chamber, and only the conveying chamber is made atmosphericpressure before taking out the wafer. The outline of Al film formationis as described above.

EXPERIMENTAL EXAMPLE 9

Al films were formed according to the method of Example 6. For the filmsobtained, the resistivity, carbon content, average wiring life,deposition speed, hillock density, generation of spike and reflectance,the same results as in Experimental example 8 were obtained.

Also, selective depositability with substrate was the same as inExperimental example 8.

EXAMPLE 7

This Example is selective deposition of Al according to the low pressureCVD method.

EXPERIMENTAL EXAMPLE 10

By means of the low pressure CVD device shown in FIG. 2, Al films wereformed on the substrates with the constitutions as described below(Samples 5-1-5-179).

Preparation of Sample 5-1

On a monocrystalline silicon as the electron donative first substratesurface material, a thermally oxidized SiO₂ film as the electronnon-donative second substrate surface material was formed, andpatterning was effected according to the photolithographic steps asshown in Example 1 to have the monocrystalline surface partiallyexposed.

The film thickness of the thermally oxidized SiO₂ film wag found to be7000 Å, with the size of the exposed portion of the monocrystallinesilicon, namely opening being 3 μm×3 μm, Thus, Sample 5-1 was prepared.(Hereinafter, such sample is expressed as "thermally oxidized SiO₂(hereinafter abbreviated as T-SiO₂)/monocrystalline silicon".

Preparation of Samples 5-2-5-179

Sample 5-2 is an oxidized film formed by normal pressure CVD(hereinafter abbreviated as SiO₂)/monocrystalline silicon.

Sample 5-3 is a boron doped oxidized film formed by normal pressure CVD(hereinafter abbreviated as BSG)/monocrystalline silicon.

Sample 5-4 is a phosphorus doped oxidized film formed by normal pressureCVD (hereinafter abbreviated as PSG)/monocrystalline silicon.

Sample 5-5 is a phosphorus and boron doped oxidized film formed bynormal pressure CVD (hereinafter abbreviated as BSPG)/monocrystallinesilicon.

Sample 5-6 is a nitrided film formed by plasma CVD (hereinafterabbreviated as P-S:N)/monocrystalline silicon.

Sample 5-7 is a thermally nitrided film (hereinafter abbreviated asT-S:N)/monocrystalline silicon.

Sample 5-8 is a nitrided film formed by low pressure CVD (hereinafterabbreviated as LP-S:N)/monocrystalline silicon.

Sample 5-9 is a nitrided film formed by ECR device (hereinafterabbreviated as ECR-SiN)/monocrystalline silicon.

Further, by combinations of the electron donative first substratesurface materials and the electron non-donative second substrate surfacematerials, Samples 5-11-5-179 shown in Table 3 were prepared. As thefirst substrate surface material, monocrystalline silicon(monocrystalline Si), polycrystalline silicon (polycrystalline Si),amorphous silicon (amorphous Si), tungsten (W), molybdenum (Mo),tantalum (Ta), tungsten silicide (WSi), titanium silicide (TiSi),aluminum (Al), aluminum silicon (Al-Si), titanium aluminum (Al-Ti),titanium nitride (TiN), copper (Cu), aluminum silicon copper (Al-Si-Cu),aluminum palladium (Al-Pd), titanium (Ti), molybdenum silicide (Mo-Si),tantalum silicide (Ta-Si) were employed. These samples and Al₂ O₃substrates, SiO₂ glass substrates were placed in the low pressure CVDdevice shown in FIG. 2, and Al films were formed within the same badge.The film forming conditions were a reaction tube pressure of 0.3 Torr, aDMAH partial pressure of 3.0×10⁻⁵ Torr, a substrate temperature of 300°C. and a film formation time of 10 minutes.

As the result of film formation under such conditions, concerning allthe samples applied with patterning from Sample 5-1 to 5-179, depositionof Al film occurred only on the electron donative first substratesurface film to embed completely the opening with the depth of 7000 Å.The film quality of the Al film was found to be very good, exhibitingthe same properties as one prepared at a substrate temperature of 300°C. shown in Experimental example 8. On the other hand, on the secondsubstrate surface which is electron non-donative, no Al film wasdeposited at all, whereby complete selectivity was obtained. On both theAl₂ O₃ substrate and the SiO₂ glass substrate which are electronnon-donative, no Al film was deposited at all.

EXPERIMENTAL EXAMPLE 11

By use of the low pressure CVD device shown in FIG. 2, Al film wasformed on the substrate with the constitution as described below.

On a thermally oxidized film as the electron non-donative secondsubstrate surface material, a polycrystalline Si as the electrondonative first substrate surface material was formed, patterning waseffected according to the photolithographic steps as shown in Example 1to have the thermally oxidized film surface partially exposed. The filmthickness of the polycrystalline silicon at this time was 2000 Å, withthe size of the thermally oxidized film exposed portion, being 3 μm×3μm. Such sample is called 6-1. By combinations of the electronnon-donative second substrate surface materials (T-SiO₂, CVD-SiO₂, BSG,PSG, BPSG, P-SiN, T-SiN, LP-SiN, ECR-S:N) and the electron-donativefirst substrate surface materials (polycrystalline Si, amorphous Si, Al,W, Mo, Ta, WSi, TiSi, TaSi, Al-Si, Al-Ti, TiN, Cu, Al-Si-Cu, Al-Pd, Ti,Mo-Si), Samples of 6-1-6-169 shown in Table 3 were prepared. Thesesamples were placed in the low CVD device shown in FIG. 2, and Al filmwas formed within the same badge. The film forming conditions were areaction tube pressure of 0.3 Torr, a DMAH partial pressure of 3.0×10⁻⁵Torr, a substrate temperature of 300° C. and a film forming time of 10minutes. As the result of film formation under such conditions, in allthe samples from 6-1 to 6-169, no Al film was deposited at all at theopening having the electron non-donative second substrate exposed, butAl of about 7000 Å was deposited only on the electron donative firstsubstrate, whereby complete selectivity was obtained. The film qualityof the Al film deposited was found to be very good, exhibiting the sameproperties as one prepared at a substrate temperature of 300° C. inExperimental example 1.

                                      TABLE 3                                     __________________________________________________________________________          Mono-                                                                             Poly-                                                                     crysta1-                                                                          Crystal-                                                                          Amor-                                                                 line                                                                              line                                                                              phous                                                                 Si  Si  Si  W  Mo Ta WSi                                                                              TiSi                                                                             Al AlSi                                      __________________________________________________________________________    T--SiO.sub.2                                                                        5-1 5-11                                                                              5-21                                                                              5-31                                                                             5-41                                                                             5-51                                                                             5-61                                                                             5-71                                                                             5-81                                                                             5-91                                      SiO.sub.2                                                                           5-2 5-12                                                                              5-22                                                                              5-32                                                                             5-42                                                                             5-52                                                                             5-62                                                                             5-72                                                                             5-82                                                                             5-92                                      BSG   5-3 5-13                                                                              5-23                                                                              5-33                                                                             5-43                                                                             5-53                                                                             5-63                                                                             5-73                                                                             5-83                                                                             5-93                                      PSG   5-4 5-14                                                                              5-24                                                                              5-34                                                                             5-44                                                                             5-54                                                                             5-64                                                                             5-14                                                                             5-84                                                                             5-94                                      BPSG  5-5 5-15                                                                              5-25                                                                              5-35                                                                             5-45                                                                             5-55                                                                             5-65                                                                             5-75                                                                             5-85                                                                             5-95                                      P--SiN                                                                              5-6 5-16                                                                              5-26                                                                              5-36                                                                             5-46                                                                             5-56                                                                             5-66                                                                             5-76                                                                             5-86                                                                             5-96                                      T--SiN                                                                              5-7 5-17                                                                              5-27                                                                              5-37                                                                             5-47                                                                             5-57                                                                             5-67                                                                             5-77                                                                             5-87                                                                             5-97                                      LP--SiN                                                                             5-8 5-18                                                                              5-28                                                                              5-38                                                                             5-48                                                                             5-58                                                                             5-68                                                                             5-78                                                                             5-88                                                                             5-98                                      ECR--SiN                                                                            5-9 5-19                                                                              5-29                                                                              5-39                                                                             5-49                                                                             5-59                                                                             5-69                                                                             5-79                                                                             5-89                                                                             5-99                                      __________________________________________________________________________                      Al--                                                              AlTi                                                                              Ti--N                                                                             Cu  Si--Cu                                                                             AlPd                                                                              Ti  Mo--Si                                                                            Ta--Si                                     __________________________________________________________________________    T--SiO.sub.2                                                                        5-101                                                                             5-111                                                                             5-121                                                                             5-131                                                                              5-141                                                                             5-151                                                                             5-161                                                                             5-171                                      SiO.sub.2                                                                           5-102                                                                             5-112                                                                             5-122                                                                             5-132                                                                              5-142                                                                             5-152                                                                             5-162                                                                             5-172                                      BSG   5-103                                                                             5-113                                                                             5-123                                                                             5-133                                                                              5-143                                                                             5-153                                                                             5-163                                                                             5-173                                      PSG   5-104                                                                             5-114                                                                             5-124                                                                             5-131                                                                              5-144                                                                             5-154                                                                             5-164                                                                             5-174                                      BPSG  5-105                                                                             5-115                                                                             5-125                                                                             5-135                                                                              5-145                                                                             5-155                                                                             5-165                                                                             5-175                                      P--SiN                                                                              5-106                                                                             5-116                                                                             5-126                                                                             5-136                                                                              5-146                                                                             5-156                                                                             5-166                                                                             5-176                                      T--SiN                                                                              5-107                                                                             5-117                                                                             5-127                                                                             5-137                                                                              5-147                                                                             5-157                                                                             5-167                                                                             5-177                                      LP--SiN                                                                             5-108                                                                             5-118                                                                             5-128                                                                             5-138                                                                              5-148                                                                             5-158                                                                             5-168                                                                             5-178                                      ECR--SiN                                                                            5-109                                                                             5-119                                                                             5-129                                                                             5-139                                                                              5-149                                                                             5-159                                                                             5-169                                                                             5-179                                      __________________________________________________________________________     (note) Numeral shows sample No.                                          

                                      TABLE 4                                     __________________________________________________________________________    Poly-                                                                         Crystal-  Amor-                                                               line      phous                              Al--                             Si        Si  W  Mo Ta WSi                                                                              TiSi                                                                             Al AlSi                                                                             AlTi                                                                             Ti--N                                                                             Cu Si--Cu                                                                            AlPd                                                                             Ti Mo--Si                                                                            Ta--Si             __________________________________________________________________________    T--SiO.sub.2                                                                        6-1 6-11                                                                              6-21                                                                             6-31                                                                             6-41                                                                             6-51                                                                             6-61                                                                             6-71                                                                             6-81                                                                             6-91                                                                             6-101                                                                             6-111                                                                            6-121                                                                             6-131                                                                            6-141                                                                            6-151                                                                             6-161              SiO.sub.2                                                                           6-2 6-12                                                                              6-22                                                                             6-32                                                                             6-42                                                                             6-52                                                                             6-62                                                                             6-72                                                                             6-82                                                                             6-92                                                                             6-102                                                                             6-112                                                                            6-122                                                                             6-132                                                                            6-142                                                                            6-152                                                                             6-162              BSG   6-3 6-13                                                                              6-23                                                                             6-33                                                                             6-43                                                                             6-53                                                                             6-63                                                                             6-73                                                                             6-83                                                                             6-93                                                                             6-103                                                                             6-113                                                                            6-123                                                                             6-133                                                                            6-143                                                                            6-153                                                                             6-163              PSG   6-4 6-14                                                                              6-24                                                                             6-34                                                                             6-44                                                                             6-54                                                                             6-64                                                                             6-74                                                                             6-84                                                                             6-94                                                                             6-104                                                                             6-114                                                                            6-121                                                                             6-134                                                                            6-144                                                                            6-154                                                                             6-164              BPSG  6-5 6-15                                                                              6-25                                                                             6-35                                                                             6-45                                                                             6-55                                                                             6-65                                                                             6-75                                                                             6-85                                                                             6-95                                                                             6-105                                                                             6-115                                                                            6-125                                                                             6-135                                                                            6-145                                                                            6-155                                                                             6-165              P--SiN                                                                              6-6 6-16                                                                              6-26                                                                             6-36                                                                             6-46                                                                             6-56                                                                             6-66                                                                             6-76                                                                             6-85                                                                             6-96                                                                             6-106                                                                             6-116                                                                            6-126                                                                             6-136                                                                            6-146                                                                            6-156                                                                             6-166              T--SiN                                                                              6-7 6-17                                                                              6-27                                                                             6-37                                                                             6-47                                                                             6-57                                                                             6-67                                                                             6-77                                                                             6-87                                                                             6-97                                                                             6-107                                                                             6-117                                                                            6-127                                                                             6-137                                                                            6-147                                                                            6-157                                                                             6-167              LP--SiN                                                                             6-8 6-18                                                                              6-28                                                                             6-38                                                                             6-48                                                                             6-58                                                                             6-68                                                                             6-78                                                                             6-88                                                                             6-98                                                                             6-108                                                                             6-118                                                                            6-128                                                                             6-138                                                                            6-148                                                                            6-158                                                                             6-168              ECR--SiN                                                                            6-9 6-19                                                                              6-29                                                                             6-39                                                                             6-49                                                                             6-59                                                                             6-69                                                                             6-79                                                                             6-89                                                                             6-99                                                                             6-109                                                                             6-119                                                                            6-129                                                                             6-139                                                                            6-149                                                                            6-159                                                                             6-169              __________________________________________________________________________     (note) Numeral shows sample No.                                          

EXAMPLE 8

This Example is the method of depositing Al selectively by use of MMAH₂.

EXPERIMENTAL EXAMPLE 12

Deposition was carried out according to the same procedure as shown inExample 1 using MMAH₂ as the starting gas and setting the conditions asfollows:

whole pressure: 1.5 Torr

MMAH₂ partial pressure: 5×10⁻⁴ Torr,

in the temperature range of the substrate temperature from 160° C. to400° C. An Al thin film containing no carbon impurity and havingexcellent flatness, denseness and selectivity with the substrate surfacematerials was deposited similarly as in Example 1.

EXPERIMENTAL EXAMPLE 13

According to the same method as in Example 5, a sample having an Al filmformed thereon was prepared. The crystallinity of the Al filmselectively deposited on Si at the same substrate temperature as inTable 1 was evaluated by the X-ray diffraction method and the scanningμ-RHEED microscope.

The scanning μ-RHEED microscope is the method disclosed in ExtendedAbstracts of the 21st Conference on Solid State Devices and Materials(1989) p. 217 and Japanese Journal of Applied Physics vol. 28, No. 11(1989), L2075. According to the RHEED (Reflection High Energy ElectronDiffraction) method of prior art, an electron beam was permitted to beincident on the sample surface at a shallow angle of 2°-3°, and thecrystallinity of the sample surface was evaluated from the diffractionpattern formed by the diffracted electron beam. However, since theelectron beam diameter is large as 100 μm to several hundred μm, onlyaverage information on the sample surface could be obtained. In theμ-RHEED microscope, an electron beam diffraction pattern from a specificfine region on the sample surface can be observed by narrowing theelectron beam diameter of 0.1 μm. Also, by scanning the electron beamtwo-dimensionally on the sample surface, by use of any desireddiffraction spot intensity change on the diffraction pattern as theimage signal, two dimensional image (scanning μ-RHEED image) on thesample surface can be obtained. At this time by observation of thescanning μ-RHEED image by use of different diffraction spots A and C onthe diffraction pattern as shown in FIG. 7, even if the lattice planesin parallel to the sample surface may be aligned in (100), the crystalgrain boundaries rotating within the plane can be visualized asdistinguished from each other. Here, the diffraction spot A is adiffraction spot on the line (line 1) where the plane in which thediffraction pattern occurs and the sagittal plane formed by the incidentelectron beam are crossed at right angle, while the diffraction spot Cis a diffraction spot not on the line 1. As shown in FIG. 8, when thelattice plane in parallel to the sample surface is, for example, (100),but crystal grains x and y are rotating mutually within the plane, inthe scanning μ-RHEED image by use of the diffraction spot A, bothcrystal grains x and y are displayed as the region with strongintensity. On the other hand, in the scanning μ-RHEED image by use ofthe diffraction spot C, only the crystal grain x is displayed as theregion with strong intensity. Therefore, by observation of the scanningμ-RHEED image by use of the diffraction spots A and C as shown in FIG.7, it can be discriminated whether the crystal in the region observed isa polycrystal including interplanar rotation or a monocrystal. InExtended Abstracts of the 21th Conference on Solid State Devices andMaterials (1989) p. 217 and Japanese Journal of Applied Physics vol. 28,No. 11 (1989) L2075, concerning Cu thin film, it has been clarifiedthat, for example, even if the lattice plane in parallel to the samplesurface may be {100}, there exists a crystal grain including interplanarrotation in the {100} crystal grains.

First, the Al film deposited selectively on the Si exposed surface atthe substrate temperature in Table 1 was evaluated.

When the crystal direction on the Si substrate surface is (111) plane,from X-ray diffraction, as shown in FIG. 9, only the diffraction peakshowing Al (100) could be observed. Next, crystallinity of the Al filmdeposited selectively was evaluated by use of a scanning μ-RHEEDmicroscope. As shown in FIG. 10, after the region where Al had beenselectively deposited was specified by the scanning secondary electronimage showing the surface form (FIG. 10A), by use of the diffractionspot 200 (corresponding to the diffraction spot A in FIG. 7) and thediffraction spot 620 (corresponding to the diffraction spot C in FIG. 7)on the diffraction pattern occurring when the electron beam waspermitted on the Al (100) plane from the 001! direction, the scanningμ-RHEED image (FIG. 10B) and FIG. 10C) was observed. As shownschematically in FIG. 10B and FIG. 10C, there is no change in lightnessand darkness on the Al film selectively deposited, and the Alselectively deposited was confirmed to be an Al (100) monocrystal.

On the other hand, when the Si exposed plane is not linear but likevia-hole, irrespectively of the through-hole diameter, the Alselectively deposited was found to be similarly Al (100) monocrystal.Those at substrate temperatures ranging from 250° C. to 330° C. wereselectively deposited stably, and the Al obtained was found to becomemonocrystal.

Also, Al films deposited selectively on the Si (111) substrate with theSi (111) plane being at off-angles by 1°, 2°, 3°, 4°, 5° from the Sisubstrate were also found to deposit Al (100) monocrystals under thetemperature conditions of the substrate temperature ranging from 250° C.to 330° C. similarly as deposited on the Si (111) substrate as describedabove.

When the crystal direction of the Si substrate surface is the (100)plane, from X-ray diffraction, as shown in FIG. 11, only the diffractionpeak showing Al (111) could be observed. FIG. 12 shows the scanningsecondary electron image (FIG. 12A) and the scanning μ-RHEED image(FIGS. 12B and 12C) when Al was selectively deposited on only the Siexposed surface on a substrate having Si (100) exposed in a line bypatterning of SiO₂ in a line. For the scanning μ-RHEED image, the 333diffraction spots (FIG. 12B) and 531 diffraction spots (FIG. 12C) wereemployed. The Al film selectively deposited was confirmed to be an Al(111) monocrystal. Those at substrate temperatures ranging from 250° C.to 330° C. were found to be selectively deposited stably, and the Alfilms obtained became monocrystals.

Also, Al films deposited selectively on the Si (100) substrate with theSi (100) plane being at off-angles by 1°, 2°, 3°, 4°, 5° from the Sisubstrate surface were also found to deposit Al (111) monocrystals underthe temperature conditions of the substrate temperature ranging from250° C. to 330 ° C. similarly as deposited on the Si (111) substrate asdescribed above.

EXPERIMENTAL EXAMPLE 14

Crystallinity of the Al film deposited selectively according to the samemethod as shown in Example 6 was evaluated. Similarly as in Experimentalexample 8, at substrate temperatures ranging from 250° C. to 330° C., Al(100) monocrystals on the Si (111) substrate and Al (111) monocrystalson Si (100) substrate were obtained stably.

EXPERIMENTAL EXAMPLE 15

Crystallinity of the Al film deposited selectively according to the samemethod as shown in Example 7 was evaluated.

From the scanning μ-RHEED microscope observation according to the sameobservation method as described in Experimental example 13, when thefirst substrate material is Si (111), in either case when the secondsubstrate material is T-SiO₂, SiO₂, BSG, PSG, BPSG, P-SiN, T-SiN, LP-SiNor ECR-SIN, the Al selectively deposited on Si was found to be Al (100).When the first substrate material is Si (100), in either case when thesubstrate material is T-SiO₂, SiO₂, BSG, PSG, BPSG, P-SiN, T-SiN, LP-SiNor ECR-SiN, the Al film selectively deposited was found to be Al (111).

When the first material is TiN, in either case when the second substratematerial is T-SiO₂, SiO₂, BSG, PSG, BPSG, P-SiN, T-SiN, LP-SiN orECR-SiN, the Al film selectively deposited on TiN was found to beoriented in Al (111) from X-ray diffraction, and from reflective highspeed electron beam diffraction pattern of the prior art by use of anelectron beam of an acceleration voltage of 80 kV or 100 kV, diffractionspots concerned with Al (111) were strongly observed.

COMPARATIVE EXPERIMENT

An Al film was formed on a monocrystalline silicon under the followingconditions.

By passing Ar in place of H₂, Al was deposited by pyrolysis of DMAH. Thetotal pressure at this time was made 1.5 Torr, the DMAH partial pressure1.5×10⁻⁴ Torr, and the substrate temperature 270°-350° C.

When the Al film thus formed was evaluated, it was found to contain atleast about 2% of carbon.

Resistivity increases by 2-fold or more than when hydrogen was employed.

As to reflectance, it was lowered to about 1/3 to 1/9 relative the casewhen hydrogen was employed.

Similarly, wiring life was shorter by 1 to 2 cipher, generationprobability of hillock became greater by 2 cipher or more, and a largenumber of spikes were found to be generated.

As to the deposition speed, it was lowered to 1/2 to 1/4.

As described above, Al deposited only by decomposition of DMAH withoutuse of H₂ is inferior in film quality, and was unsatisfactory as the Alfilm for a semiconductor device.

Separately, without use of H₂, DMAH was decomposed by the optical CVDmethod to deposit Al. As the result, some improvement such as nocontamination by carbon, and the like was observed from the Al filmprepared as compared with the case when no light was employed, but othercharacteristics were not improved, and the Al film was stillunsatisfactory as the Al film for a semiconductor device.

As described above, the mechanism of Al deposition according to thepresent invention may be presently hypothesized as follows.

When DMAH reaches the electron donative substrate, namely the substratehaving electrons under the state on which hydrogen atoms are attached(FIG. 13A) with the methyl groups directed toward the substrate side,one electron of the substrate cuts one bond of the Al and methyl group(FIGS. 13B, 13C).

The reaction scheme at this time is as follows:

    (CH.sub.3).sub.2 AlH+2H+2e→2CH.sub.4 ↑+Al-H

Further, similar reactions will proceed for the hydrogen atoms remainingon deposited Al having free electrons (FIG. 13D). Here, when hydrogenatoms are deficient, hydrogen molecules constituting the reaction gasare decomposed on the substrate to supply hydrogen atoms. On the otherhand, since there is no electron on the electron non-donative surface,the above-mentioned reaction will not proceed and no Al is deposited.

FIGS. 13A-13D are illustrations for better understanding of the reacionmechanism, and the numbers of H, e and Al shown in FIGS. 13A-13D are notnecessarily coincident.

As described above, according to the present invention, a lowresistivity, dense and flat Al film can be deposited on a substrate.

Also, depending on the kind of the substrate, deposition can be effectedselectively.

What we claim is:
 1. A method for selectively forming an aluminum thinfilm, comprising the steps of:forming on a silicon substrate an oxidizedfilm mask having an opening and introducing dimethyl aluminum hydride asa starting gas onto the silicon substrate by a chemical vapor depositionmethod to selectively deposit an aluminum thin film only on a siliconsurface exposed from the opening.
 2. A chemical vapor deposition methodfor depositing a metal film containing aluminum on a substrate providedin a chamber for formation of a deposited film, comprising the stepsof:(a) maintaining the pressure inside the chamber at a pressure withinthe range from 10⁻³ to 760 Torr; (b) introducing a gas of alkyl aluminumhydride and hydrogen gas into the chamber sufficient to provide apartial pressure of the gas of alkyl aluminum hydride from 1.5×10⁻⁵ to1.3×10⁻³ of the pressure inside the chamber; and (c) maintaining asubstrate temperature sufficient to decompose said alkyl aluminumhydride to deposit a metal film containing aluminum on a conductive orsemiconductive surface of the substrate.
 3. A chemical vapor depositionmethod for depositing a metal film containing aluminum on a plurality ofsubstrates provided in a chamber for formation of a deposited film,comprising the steps of:(a) maintaining the pressure inside the chamberat a pressure within the range from 10⁻³ to 760 Torr; (b) introducing agas of alkyl aluminum hydride and hydrogen gas into the chambersufficient to provide a partial pressure of the gas of alkyl aluminumhydride from 1.5×10⁻⁵ to 1.3×10⁻³ of the pressure inside the chamber;and (c) maintaining a plurality of substrates at a temperaturesufficient to decompose said alkyl aluminum hydride to deposit a metalfilm containing aluminum on a conductive or semiconductive surface ofeach one of the plurality of substrates.
 4. A chemical vapor depositionmethod for depositing a metal film containing aluminum on a substratehaving an insulating surface and a semiconductive surface or aconductive surface provided in a chamber for formation of a depositedfilm, comprising the steps of:(a) maintaining the pressure inside thechamber at a pressure within the range from 10⁻³ to 760 Torr; (b)introducing a gas of alkyl aluminum hydride and hydrogen gas into thechamber sufficient to provide partial pressure of the gas of alkylaluminum hydride from 1.5×10⁻⁵ to 1.3×10⁻³ of the pressure inside thechamber; and (c) maintaining a substrate temperature sufficient todecompose said alkyl aluminum hydride to selectively deposit a metalfilm containing aluminum on the semiconductive surface or the conductivesurface of the substrate.
 5. A chemical vapor deposition method fordepositing a metal film containing aluminum on a plurality of substrateseach having an insulating surface and a semiconductive surface or aconductive surface provided in a chamber for formation of a depositedfilm, comprising the steps of:(a) maintaining the pressure inside thechamber at a pressure within the range from 10⁻³ to 760 Torr; (b)introducing a gas of alkyl aluminum hydride and hydrogen gas into thechamber sufficient to provide a partial pressure of the gas of alkylaluminum hydride from 1.5×10⁻⁵ to 1.3×10⁻³ of the pressure inside thechamber; and (c) maintaining the substrate temperature sufficient todecompose said alkyl aluminum hydride to selectively deposit a metalfilm containing said aluminum on the semiconductive surface or theconductive surface of the plurality of substrates.
 6. The chemical vapordeposition method according to any one of claims 2 to 5, wherein thealkyl aluminum hydride is dimethyl aluminum hydride.
 7. A chemical vapordeposition method for depositing a metal film containing aluminum on asubstrate provided in a chamber for formation of a deposited film,comprising the steps of:(a) maintaining the pressure inside the chamberat a pressure within the range from 10⁻³ to 760 Torr; (b) introducing agas of alkyl aluminum hydride and hydrogen gas into the chamber; and (c)maintaining a substrate temperature sufficient to decompose said alkylaluminum hydride to deposit a metal film containing aluminum on aconductive or semiconductive surface of the substrate, the conductive orsemiconductive surface comprising a metallic nitride.
 8. A chemicalvapor deposition method for depositing a metal film containing aluminumon a plurality of substrates provided in a chamber for formation of adeposited film comprising the steps of:(a) maintaining the pressureinside the chamber at a pressure within the range from 10⁻³ to 760 Torr;(b) introducing a gas of alkyl aluminum hydride and hydrogen gas intothe chamber; and (c) maintaining a plurality of substrates at atemperature sufficient to decompose said alkyl aluminum hydride todeposit a metal film containing aluminum on a conductive orsemiconductive surface of each one of the plurality of substrates, theconductive or semiconductive surface comprising a metallic nitride.
 9. Achemical vapor deposition method for depositing a metal film containingaluminum on a substrate having an insulating surface and asemiconductive surface or a conductive surface provided in a chamber forformation of a deposited film, comprising the steps of:(a) maintainingthe pressure inside the chamber at a pressure within the range from 10⁻³to 760 Torr; (b) introducing a gas of alkyl aluminum hydride andhydrogen gas into the chamber; and (c) maintaining a substratetemperature sufficient to decompose said alkyl aluminum hydride toselectively deposit a metal film containing aluminum on thesemiconductive surface or the conductive surface of the substrate, theconductive or semiconductive surface comprising a metallic nitride. 10.A chemical vapor deposition method for depositing a metal filmcontaining aluminum on a plurality of substrates each having aninsulating surface and a semiconductive surface or a conductive surfaceprovided in a chamber for formation of a deposited film, comprising thesteps of:(a) maintaining the pressure inside the chamber at a pressurewithin the range from 10⁻³ to 760 Torr; (b) introducing a gas of alkylaluminum hydride and hydrogen gas into the chamber; and (c) maintainingthe substrate temperature sufficient to decompose said alkyl aluminumhydride to selectively deposit a metal film containing said aluminum onthe semiconductive surface or the conductive surface of the plurality ofsubstrates, the conductive or semiconductive surface comprising ametallic nitride.
 11. A chemical vapor deposition method for depositinga metal film containing aluminum on a substrate provided in a chamberfor formation of a deposited film, comprising the steps of:(a)maintaining the pressure inside the chamber at a pressure within therange from 10⁻³ to 760 Torr; (b) introducing a gas of dimethyl aluminumhydride and hydrogen gas into the chamber; and (c) maintaining asubstrate temperature sufficient to decompose said dimethyl aluminumhydride to deposit a metal film containing aluminum on a conductive orsemiconductive surface of the substrate, the conductive orsemiconductive surface comprising titanium nitride.
 12. A chemical vapordeposition method for depositing a metal film containing aluminum on aplurality of substrates provided in a chamber for formation of adeposited film, comprising the steps of:(a) maintaining the pressureinside the chamber at a pressure within the range from 10⁻³ to 760 Torr;(b) introducing a gas of dimethyl aluminum hydride and hydrogen gas intothe chamber; and (c) maintaining a plurality of substrates at atemperature sufficient to decompose said dimethyl aluminum hydride todeposit a metal film containing aluminum on a conductive orsemiconductive surface of each one of the plurality of substrates, theconductive or semiconductive surface comprising titanium nitride.
 13. Achemical vapor deposition method for depositing a metal film containingaluminum on a substrate having an insulating surface and semiconductivesurface or a conductive surface provided in a chamber for formation of adeposited film, comprising the steps of:(a) maintaining the pressureinside the chamber at a pressure within the range from 10⁻³ to 760 Torr;(b) introducing a gas of dimethyl aluminum hydride and hydrogen gas intothe chamber; and (c) maintaining a substrate temperature sufficient todecompose said dimethyl aluminum hydride to deposit selectively a metalfilm containing aluminum on the semiconductive surface or the conductivesurface of the substrate, the conductive or semiconductive surfacecomprising titanium nitride.
 14. A chemical vapor deposition method fordepositing a metal film containing aluminum on a plurality of substrateseach having an insulating surface and a semiconductive surface or aconductive surface provided in a chamber for formation of a depositedfilm, comprising the steps of:(a) maintaining the pressure inside thechamber at a pressure within the range from 10⁻³ to 760 Torr; (b)introducing a gas of dimethyl aluminum hydride and hydrogen gas into thechamber; and (c) maintaining the substrate temperature sufficient todecompose said dimethyl aluminum hydride to selectively deposit a metalfilm containing said aluminum on the semiconductive surface or theconductive surface of the plurality of substrates, the conductive orsemiconductive surface comprising titanium nitride.